Electron temperature is typically measured using the relative line ratio in emission spectrum of characteristic lines or by measuring the bremsstrahlung continuum shape. The ion temperature is measured from the broadening of spectral lines, typically in the x-ray. Sandia National Lab had a huge affair a few years back about 200 keV ion temperatures in iron plasmas. There is a PRL published by Malcolm Haines of Imperial College about it. The debate about the source rages to this day.
Electron heating and cooling: To get an ion hot, you must undergo many, many collisions with electrons that have more energy but each transfer is small because of momentum conservation so only a fraction of the electron population can supply energy to the ion. In the case of cooling, the electrons collide with the ion and take a fraction of the energy. The electrons radiate the energy away as brems when they slow. Those greedy electrons go back for more. While many electrons take away energy only some can provide it. The electrons also transport energy (heat) very efficiently as they are highly mobile. A typical pinch has a temperature profile with the temperature peaked near the center. If electrons are able to move, they transport that heat out of the core plasma to the edge.
The general rule of plasma is the electrons are the dominate particles for energy transport, radiation and current carrying. The ions are responsible for momentum carrying and mass. These rules are pretty universal. Pinches are a bit funny as the ions have such large kinetic energies before the pinch implodes which allows them to have large ion temperatures when the pinch stagnates on axis. Other plasma systems cannot give the ion much energy as they are slow to respond to electric fields unlike electrons and they are so heavy. The PF allows the ions to move quickly due overwhelming magnetic pressure behind the plasma sheath that pushes both the ions and electrons at the same speed. If an ion moves at the same speed as an electrons but has 2000X the mass, it has 2000X the energy. Easy to see how the ion can have higher temperatures than the electrons in a pinch. The thermalization is complex so don’t read too much in the 2000X number upfront. Those pursuing fusion wish that cold electrons could coexist with hot ions.
Can’t speak to the onion or LPP’s plans for it.